1. Field of Invention
The present invention relates to an impact energy absorbing structure formed in an upper portion of a body of a motor vehicle, and to an impact energy absorbing component. More particularly, the invention relates to an impact energy absorbing structure formed in an upper vehicle body portion including a vehicle body structural member, such as a pillar, a roof side rail, a header or the like, and an interior trim, such as a pillar garnish, a roof lining or the like, that is spaced from the structural member by an interval extending toward the interior of a passenger compartment, wherein an energy absorbing member is disposed within the interval, and also relates to an impact energy absorbing component for use in the impact energy absorbing structure.
2. Description of Related Art
In motor vehicles, particularly, in passenger cars, an energy absorbing member is disposed in a space between an interior trim and a structural member of a vehicle body. Therefore, if an impact load is applied in a direction from the interior trim to the structural member, the energy absorbing member deforms to absorb energy of the impact load. Normally employed energy absorbing members are, for example, a grid rib member, a urethane pad, a steel member formed by bending a thin steel sheet so as to have a hat-like sectional shape, and the like. Also employed as an energy absorbing member is a generally-termed hybrid pipe (as described in U.S. Pat. No. 5,680,886) that is made up of a metal foil core member and sheets of a material other than metal that are laid on opposite side surfaces of the core member. In the hybrid pipe, the core member and the sheets on the opposite side surfaces of the core member are corrugated so that ridges and grooves alternate in a direction of a longitudinal axis of the pipe.
A hybrid pipe, after being formed, can easily be changed into a desired sectional shape by correspondingly shaping the pipe. Furthermore, the energy absorption characteristics of a hybrid pipe can be adjusted by changing a thickness of the hybrid pipe measured between an outermost point in the curved outer surface of a ridge or protruded portion and an innermost point in the curved inner surface of a groove or recessed portion, that is, the generally-termed apparent plate thickness of the hybrid pipe, or by changing the pitch between adjacent protruded portions (or recessed portions), or the like. Thus, a hollow-shaped energy absorbing member represented by a hybrid pipe or the like has good properties desirable for an energy absorbing member.
Vehicle body structural members to be installed at certain locations in a vehicle body are formed into three-dimensionally bent shapes in order to meet strength and design requirements. In some locations, therefore, it is difficult to dispose an energy absorbing member so as to extend precisely conforming to the shape of an adjacent structural member. Interior trims are normally formed mainly to meet design needs, and the need to conform an interior trim to a local shape of an adjacent structural member is rather minor. Therefore, if a hybrid pipe or a different hollow pipe is disposed in an interval between a structural member and an interior trim, there may be a gap formed between the structural member and the energy absorbing member or between the energy absorbing member and the interior trim, the gap extending in directions of the length of the structural member and varying in size with progress in those lengthwise directions.
An energy absorbing member preferably starts deforming during an initial period following occurrence of an impact load, and absorbs a designed amount of energy as it is displaced to a predetermined amount of displacement. However, if there is a gap between the energy absorbing member and an interior trim or a structural member, the energy absorbing member does not deform until the gap is eliminated. The aforementioned predetermined amount of displacement of an energy absorbing member means an amount of displacement to which the energy absorbing member can be displaced while being deformed by an impact load. The predetermined amount of displacement is substantially constant. Therefore, if there is a gap between the energy absorbing member and the structural member or the interior trim, an impact load will move the energy absorbing member to an amount of displacement corresponding to the size of the gap without deforming the energy absorbing member, so that the effective displacement of the energy absorbing member caused by the impact load decreases and the amount of energy absorbed correspondingly decreases. Thus, if a gap exists between an energy absorbing member and an interior trim or a structural member, and the size of the gap varies in directions of length of the structural member, the amount of energy absorbed becomes likely to greatly vary depending on the site of impact load.